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16 January, 17:10

If the speed of air flow past the lower wing of and airplane is 350 ft/s, what speed of flow over the upper wing will produce a lift of 20 lb/ft^2?

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  1. 16 January, 17:39
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    We shall apply Bernouli's theorem

    ρgh + 1/2 ρ v² + P = constant

    ρ is density of fluid (here it is air) v is velocity of air, P is pressure of air

    For h to be constant

    1/2 ρ v² + P = constant

    1/2 ρ₁ v₁² + P₁ = 1/2 ρ₂ v₂² + P₂

    P₂ - P₁ = 1/2 ρ₁ v₁² - 1/2 ρ₂ v₂²

    P₂ - P₁ = Pressure difference = 20 x 32

    ρ₁ and ρ₂ are same here and is equal to. 07967 lb/ft³

    Putting the values we get

    20 x 32 = 1/2 x. 07967 (v₁² - v₂²)

    (v₁² - v₂²) = 16066

    v₂ = 350 ft/s

    v₁²-350² = 16066

    122500 + 16066 = v₁²

    v₁² = 138566

    v₁ = 372 ft/s

    [ At lower wing velocity will be lower so that pressure will be higher.]
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